1. Field of the Invention
This invention relates to a process for attaining anti-fouling of a constantly water-contacting surface of an article against deposition of water micro-organisms by the use of organo-tin compounds. It relates also to an article capable of providing such anti-fouling characteristic.
2. Description of the Prior Art
As the articles of the above kind, fishing and fish-cultivating nets, floats, boat hulls, fishery tools, ropes and the like can be mentioned.
When water micro-organisms such as barnacle, serpula, polyzoan, mussel, ascidian, laver, green laver and/or the like are attached onto the surface of a water-immersed article and grow thereover, the mechanical strength as well as the durable life of the article may be substantially reduced, as is very well known. In addition, especially in the case of fishing nets, the fluid resistance for the in- or out-flowing water through the meshes of the net becomes larger and larger, whereby in the case of fish cultivation in a limited area of the sea, for instance, in an area surrounded by such a net, the fishes under cultivation are adversely affected by a poor supply of oxygen dissolved in the water. In the case of a fishing net, the increases flow resistance gives rise to substantially increased man power needs for the fishery.
In order to minimize these drawbacks, fishing nets and the like articles floating on or immersed in the water must be frequently dried under daylight so as to kill the deposited and flourishing water micro-organisms, thus causing a large amount of additional man power to be consumed for this purpose and substantial mechanical damage of the net. These are sincere and grave troubles to the fishermen.
In the case of the culture of oysters and the like shellfish, the deposit of water micro-organisms on the suspension ropes and floats of the culturing net will invite an increased weight thereof and the dipping depth of the suspended culture net will be correspondingly increased, which adversely affects the growth of the oysters. In the case of the fixed fishing net, the same cause as above referred to will reduce the yield of caught fish.
In order to avoid these conventional drawbacks, it has already been proposed to use inorganic anti-fouling agents such as cuprous oxide, mercury oxide or the like; organo-copper salts such as copper naphthenate, copper oleate or the like; an organo-tin compound such as bis-tributyl tin oxide, independently or in combination, so as to prevent deposition of water micro-organisms on the articles exposed to sea or river water. These substances are highly poisonous and known especially as effective agents of ship bottom anti-fouling paint. With use of these anti-fouling substances, various disadvantages have been encountered. As an example, the material of the articles to be protected has been found substantially deteriorated or damaged by the aggression of these agents per se, or of the modified substances therefrom in the presence of industrial fouling substances dissolved in the water. A further considerable disadvantage derived from the use of these conventional anti-fouling agents is such that these can be applied only through a coating technique. Especially, a uniform coating of these substances is highly difficult. In addition thereto, with the use of the developer as employed in the coating application of these anti-fouling agents, it has been frequently encountered that the developer is rather liable to dissolve into the water and the anti-fouling agent may frequently be scaled off from the applied article surface. On the other hand, when the developer is difficult to dissolve, the water-immersed article, such as fishing net and fishery rope, is liable to become stiffened and the anti-fouling agent is frequently scaled off within an unexpectedly short period.